In welding joints or filling gaps along a predetermined path between work pieces, such as flat or curved plates, bars, etc., in edge-to-edge or in cornered relationship, and in joining annular parts such as large pipe sections together in end-to-end relationship, it has been a common practice to move a welding heat source, such as an arc welding torch or like instrument along a predetermined weld path, relative to the work, while fusing and depositing filler metal in the gap from a consumable electrode source. A supply of wire electrode is commonly used as filler material. To produce welds of high quality, the deposited metal must be well and uniformly bonded to the underlying metal and to the respective walls or side elements. Welding machines have been designed to travel in accurately guided paths, but at best, precise and continuous alignment with the weld path is difficult to achieve. Also, where the gap or space to be filled is of appreciable width, it is common practice to reciprocate or oscillate the arc or other heat source laterally back and forth across the main travel path as it travels along the main or predetermined path. Accurate control of the amplitude of such lateral movement is often difficult to achieve, although various methods to do so have been proposed in U.S. Pat. Nos. 3,748,433, 3,775,582, 3,777,115, 3,832,522, and others. It is difficult, also, to keep the welding head or torch travelling with precision along the centerline of the weld path, even though many devices have been proposed for this purpose, as in several U.S. patents, including Nos. 3,084,246, 3,268,707, 3,855,446, and others. Other proposals have been made to correct certain other welding variables by using signals generated in the process to initiate correction as in U.S. Pat. Nos. 3,646,309 and 3,646,311. None of these, however, is suitable for the particular purposes of the present invention.
In recent years, electric arc welding devices, which are relatively small and light in weight and which, under favorable conditions, are capable of making high precision welds have been developed and used quite successfully. As long as they are operated by highly skilled operators, their performance usually is satisfactory. One example of equipment designed particularly for welding annular pipe joints, is described in U.S. Pat. No. 3,806,694. However, even the best of these devices may tend to wander from a true centerline path at times and their oscillation patterns or amplitudes are not always suitable for high quality welds. This is particularly true when the operators are not alert or skillful to observe and correct early minor trends towards misalignment or improper oscillation amplitude. Even with the best of equipment, faulty welds may result from minor deviations from an optimum weld path and/or by an improper oscillation amplitude. An object of the present invention is to monitor and/or to avoid or correct such faults.
As will be explained further, below, the invention is broadly applicable to control of welding instrument position alongside a single upraised wall. In the more common case, which will be further explained, the instrument is to be moved along a gap between two parallel spaced upraised walls for depositing metal in the gap between them.
Another object of the present invention is to design equipment that will be kept automatically in precise path alignment and/or will maintain optimum lateral travel paths, without requiring constant attention and control by a skilled human operator. A more particular object is to make available relatively simple equipment, of small size and mass, which can be incorporated into existing commercial welding devices, such as that described in the above mentioned U.S. Pat. No. 3,806,694, although the invention is by no means limited to pipeline welding. Other objects and advantages will be manifest after the following detailed description is given and understood.